1. Field of the Invention
The present invention relates generally to a planar antenna, and in particular to a feed point adjustable planar antenna.
2. The Prior Arts
A primary function of an antenna is to convert electromagnetic radiation energy in a transmission medium (usually air) and energy transmitted or received by a transceiver. During a process of energy transformation, discontinuous interfaces may occur between the transceiver and the antenna and between the antenna and the transmission medium. In a wireless communication system, the antenna needs to be designed according to characteristics of the two interfaces so that a continuous energy transmission path may be formed between the transceiver, the antenna and the transmission medium. Thus, a transmitting antenna can radiate energy of a transmitter to the transmission medium and a receiving antenna can transmit the energy of the electromagnetic radiation to the receiver.
There are many variations of antennas, such as dual-polarized antennas, helix antennas, planer inverted F antennas (PIFA), microstrip antennas, etc. The PIFA can achieve impedance matching without including extra inductance and capacity so it becomes increasingly popular.
The PIFA gets its name since its side view looks like an inverted letter “F”. On one hand, because an operation length of the PIFA is only ¼ of an operation wavelength and the PIFA already includes a ground metal plane, the sensitivity to the ground metal plane in a module may be reduced. Thus, the PIFA is suitable for a Bluetooth module device. On the other hand, the PIFA only needs a metal conductor cooperating with an appropriate feed and antenna being short circuited to a position of the ground plane. Thus, its cost is low and the PIFA can be welded to a printed circuit board directly.
Generally, a size of an antenna component is changed to fine tune a frequency band interval according to different environment. However, in order not to affect the performance of the antenna, the sizes of different components cannot be drastically changed. Thus, the tuning is limited. In some cases, such as fluctuation of size parameters being too wide, even the size is changed, and it is still hard to meet an actual requirement. At the same time, in order to test the fine tuning, a part of the antenna is cut each time to test whether the requirement is met. If the requirement is not met, the antenna is cut again until the requirement is met. Therefore, although the method mentioned above is effective, it is time consuming and expensive. It is not an optimal method of fine tuning.
In order to solve the problem of fine tuning, a method for fine tuning is proposed in which the feed point of a coaxial cable is changed while the size of the antenna is not changed. However, in the structure of the antenna, a ground pin electrically connecting a radiation component and a ground component extends from a middle portion of a side of the ground component to the radiation component, which limits a coupling range between the radiation component and the ground component and further limits the feed position of the coaxial cable.